Globalization, drug resistance, and bioterrorism all contribute to the growing threat from infectious diseases, but despite medical advances, we are often still unable to rapidly protect non-immune populations. Passive immunotherapy is a fast and successful method of protection, but monoclonal antibodies (mAbs) are expensive and require high, repeated doses to be effective. Therefore, this approach is not suitable for large-scale use. The delivery of mAbs using a viral vector has been recently proposed as an attractive alternative to the direct injection of mAbs. To this end, a variety of viral vectors have been used to express mAbs; however, vector immunity and safety issues have hampered the development of this strategy. The main of objective of this proposal is to address the feasibility of using integrase-defective lentiviral vectors (IDLV) to deliver mAbs. IDLV have several advantages over other viral vectors, including the absence of pre-existing anti-vector immunity and the safety features of non-integration and non-replication. IDLV are also maintained in non-dividing cells, and can express steady levels of functional proteins in vivo for months. As proof of the feasibility of using IDLV to express mAbs that protect against infectious disease, we will engineer IDLV to express mAbs against the influenza A virus (IAV) hemagglutinin (HA), and will test their ability to protect against IAV infection. An advantage of using IAV as a model is that HA-specific antibody- mediated mechanisms of protection are well-defined. Furthermore, both passive immunization and hyperimmune sera have been successfully used to prevent and treat IAV. In our preliminary data, we show that IDLV can express anti-HA mAbs in vitro in transduced cells, and we quantify the levels. Based on an estimate of the amount of mAbs needed for protection, we hypothesize that IDLV will produce an adequate level of mAbs to protect against IAV challenge in mice. In addition, since we showed that IDLV expressing influenza NP could elicit protective immunity against IAV, we will test the effectiveness of combining the genetic delivery of a mAb and a conserved influenza antigen to protect against IAV. We will test our hypothesis through the following aims: 1. measure the levels and persistence of mAbs produced from IDLV in the serum or lungs of mice and determine the optimal dose for use in challenge experiments, 2. assess the ability of IDLV expressing anti-HA mAbs to protect against lethal IAV challenge, and 3. evaluate the ability of co-administration of IDLV expressing anti-HA mAbs and IDLV expressing NP to protect from IAV at different times after administration. If successful, our study would be the first to show the effectiveness of IDL as a tool for genetic delivery of mAbs that protect against infectious agents. Additionally, expression of mAbs along with a protective antigen is a novel application in disease prevention that could have a broad impact on the prevention of IAV and other infectious diseases. Given the safety feature of non-integration, the successful development of this vector would represent a significant step in gene delivery and vaccine development.